Immediate-or-cancel order

An immediate-or-cancel order fills whatever quantity it can right away and automatically cancels whatever portion remains unfilled, rather than leaving the rest of the order open to fill later. If an investor places an immediate-or-cancel order for one thousand shares and only six hundred are available at the specified price at that instant, six hundred shares fill immediately and the remaining four hundred are simply canceled instead of sitting in the order book waiting.

This makes immediate-or-cancel different from an all-or-none order, which insists on the full quantity but is willing to wait for it, and from a fill-or-kill order, which insists on both the full quantity and instant execution. An immediate-or-cancel order takes whatever it can get immediately, partial fills included, and gives up on the rest rather than continuing to search for more or requiring the whole amount at once.

Traders use immediate-or-cancel orders when they want a quick read on how much size is actually available at a given price without leaving a resting order exposed in the book, since a resting order can signal trading intentions to others or risk filling later at a price the trader no longer wants. It is common in algorithmic and institutional trading strategies that probe for available liquidity in small, fast steps rather than committing to one large order all at once.